1. Field of the Invention
This invention concerns the use of electrodialysis for the separation and concentration of ions from radioactive waste (radwaste) solutions. In particular it is directed to employing a plurality of electrochemical and electrodialysis units or stacks in a novel combination to concentrate radioactive cations from low level acidic solutions that result from dissolving irradiated fuel from nuclear reactors in solvents such as nitric acid.
2. Prior Art
The removal, separation and/or recovery of radioactive ions from waste solutions by employing ion-exchange resin columns is well known in the art. U.S. Patents disclosing the use of ion-exchange resin are for example Nos. 4,434,138 4,423,159, 4,423,008, 4,397,819, 4,312,838, 2,752,309, 2,554,649 and many others. However, the absorption by ion-exchange is an expensive process and in practice is applicable to solutions which are very slightly loaded with salt ions. Additionally ion-exchange resin operation requires regeneration or replacement of the exhausted resin.
It is further known that electrodialysis can be employed to separate out cesium, cerium, zirconium and uranium values from each other. U.S. Pat. No. 3,038,844 describes a method and apparatus for this purpose. However, such disclosed process employs a single electrodialysis stack which does not result in obtaining a sufficiently high deacidification and/or decontamination factor and which generally operates at a low current efficiency.